1. Field of the Invention
This invention relates to a detector for the detection of anomalies in pipelines which transport liquids. In its preferred embodiment, the invention relates to a sensor unit which is capable of inspecting a liquid-transporting pipeline, without interfering with the transported liquids in the pipeline. In one embodiment, the detector locates liquid leaks where liquid is escaping from the pipeline from the pipeline. In another embodiment, the detector is used in a concrete pipeline with wire reinforcement, and detects corroded or damaged portions of the wire reinforcement, or is used in a metal pipeline and detects corrosion and/or weld failures. The sensor unit also has a novel way of determining its location within the pipeline.
2. Description of the Prior Art
It is known to use acoustic detectors to detect leaks in a pipeline. Detectors can, for example, be placed on the underside of inspection ports, or they can be placed along a cable strung between inspection ports, or along a cable allowed to trail along the lowest portion of the pipe, as shown in Paulson Canadian Patent no. 2,273,979. Such detectors can detect the sound made by a breaking wire reinforcement in a wire-reinforced concrete pipeline, or can detect the sound of liquid escaping through a leak in a metal or concrete pipeline.
It is known to inspect small diameter pipelines, particularly oil pipelines, using a device called a “pig”, which fills the pipeline and is propelled along it by oil pressure. Such inspection can be used to locate leaks and to check the welds between adjacent lengths of pipe.
It is also known to inspect pipelines with a neutral density untethered sensor, which is propelled by the liquid of the pipeline, such as is shown in PCT Published Application WO 2004/059274. However, it is difficult to tell the location of such a sensor within the pipeline, and the sensor is subject to getting trapped within the pipeline. Further, such sensor units communicate with electromagnetics, which prevents it from using magnetic sensors such as magnetometers to sense pipeline conditions.
If a pipeline is large enough (for example, large concrete pipes to bring water to cities or large sewer pipes) the pipe can be drained and a human can conduct a manual inspection. Some types of inspection are also known in drained pipelines using sensors mounted on a wheeled cart or the like. See for example, Paulson U.S. Pat. No. 6,781,369.